A catalytic hydrocarbon fuel reformer converts a fuel stream comprising, for example, natural gas, light distillates, methanol, propane, naphtha, kerosene, gasoline, diesel fuel, bio-diesel or combinations thereof, and air, into a hydrogen-rich reformate fuel stream comprising a gaseous blend of hydrogen, carbon monoxide, and nitrogen (ignoring trace components). In a typical reforming process, the raw hydrocarbon is percolated with oxygen in the form of air through a catalyst bed or beds contained within one or more reactor tubes mounted in a reformer vessel. The catalytic conversion process is typically carried out at elevated catalyst temperatures in the range of about 700° C. to about 1100° C.
The produced hydrogen-rich reformate stream may be used, for example, as the fuel gas stream feeding the anode of an electrochemical fuel cell. Reformate is particularly well suited to fueling a solid-oxide fuel cell (SOFC) system because a purification step for removal of carbon monoxide is not required as is the case for a proton exchange membrane (PEM) fuel cell system.
The reformate stream may also be used in spark-ignited (SI) or diesel engines. Reformate can be a desirable fuel or fuel-additive; the reformate stream also can be injected into the vehicle exhaust to provide benefits in reducing vehicle emissions. Hydrogen-fueled vehicles are of interest as low-emissions vehicles because hydrogen as a fuel or a fuel additive can significantly reduce air pollution and can be produced from a variety of fuels. Hydrogen permits a SI engine to run with very lean fuel-air mixtures that greatly reduce production of NOx. As a gasoline additive, small amounts of supplemental hydrogen-rich reformate may allow conventional gasoline-fueled internal combustion engines to reach nearly zero emissions levels. As a diesel fuel additive, supplemental reformate may enhance operation of premixed combustion in diesel engines. Reformate can be injected into the vehicle exhaust stream to improve NOx reduction and/or as a source of clean chemical energy for improved thermal management of exhaust components (for example, NOx traps, particulate filters and catalytic converters).
Fuel/air mixture preparation constitutes a key factor in the reforming quality of catalytic reformers, and also the performance of porous media combustors. A problem in the prior art has been how to vaporize fuel completely and uniformly, especially at start-up when the apparatus is cold. Inhomogeneous fuel/air mixtures can lead to decreased reforming efficiency and reduced catalyst durability through coke or soot formation on the catalyst and thermal degradation from local hot spots. Poor fuel vaporization can lead to fuel puddling, resulting in uncertainty in the stoichiometry of fuel mixture. Complete and rapid fuel vaporization is a key step to achieving a homogeneous gaseous fuel-air mixture.
Fuel vaporization is especially challenging under cold start and warm-up conditions for a fuel reformer. In the prior art, it is known to vaporize injected fuel by preheating the incoming air stream to be mixed with the fuel, or by preheating a reformer surface for receiving a fuel spray. However, none of the prior art approaches is entirely successful in providing reliable, complete vaporization of injected liquid fuel.
What is needed is a method and apparatus for rapidly heating and vaporizing liquid hydrocarbon fuel injected into a reformer assembly, even when the overall assembly is in a cold start-up condition.
It is a primary object of the invention to prevent coking of the housing and catalyst of a hydrocarbon reformer, especially at start-up of the reformer.